APPENDIX B
U-234 AND U-236 MASS INVENTORY SENSITIVITY

The initial fuel composition of some reactor fuels may contain specifications for U-234 and/or U-236 in addition to the usual specifications for U-235 and U-238. It is the purpose of this appendix to evaluate the effect that U-234 and U-236 have on the overall fuel assembly mass inventory when these isotopes are or are not included in the initial fuel assembly composition.

A comparison of the fuel mass inventory for a HEU and a LEU fuel composition, with and without initial enrichments of U-234 and U-236, are shown in Table B1. Typical enrichments of U-234 and U-236 in research reactor fuels are less than 1%; these specific data are for typical TRIGA fuel compositions.

The upper section of Table B1 shows the mass inventory for HEU and LEU fuels with initial enrichments of U-234 and U-236, and the lower section shows similar data for the same fuels but without initial U-234 and U-236 enrichment. The result of this comparison shows that to first-order, any initial mass of U-234 or U-236 can be simply added to the mass inventory for U-234, U-236 and total U at any burnup level. The mass inventory for Np-237 and Pu-238 which are also functions of the U-236 mass, are not substantially affected by an initial enrichment of U-236.

• Table B1 - TRIGA Fuel 25-Rod Cluster Model